This invention relates in general to seating and, more particularly, to a device for providing a seating surface with a desired contour and to a seating arrangement formed with the device.
The typical wheelchair has side frames which move together to enable the chair to be reduced to a more compact configuration--one suitable for storage or transport. To accommodate this conversion, the typical wheelchair has attached to its side frames a sling-type seat, which being flexible, simply folds upon itself as the side frames move together. While the sling-type seat nicely facilitates the conversion between open and closed positions, it does not serve the occupant's needs in other more important respects. Such seats become uncomfortable after prolonged periods, and much worse, concentrate the occupant's weight at the bony protuberances of the buttocks, thus inducing decubitus ulcers, more commonly known as bed sores.
The problem resides primarily in the inherent curvature of the sling-type seat--a generally uniform curvature which resembles that of a hammock. It tends to urge the occupant's thighs together, making them difficult to spread, particularly for one so crippled as to be confined to the wheelchair. While the seat has flexibility, it has little resiliency in the vertical direction and as a consequence most of the occupant's weight is transferred to the seat in the region of the bony protuberances of the buttocks. Without the circulation induced by movement, decubitus ulcers may well develop in the region of the bony protuberances.
Cellular cushions, such as those disclosed in U.S. Pat. Nos. 4,005,236 and 4,541,136 of R. H. Graebe, substantially reduce the incidence of decubitus ulcers from wheelchair occupancy. These cushions interpose a multitude of air cells between the sling-type seat and the buttocks of the occupant, and these air cells deflect to accommodate the contour of the occupant's body. Since the air cells are interconnected, each cell exerts essentially the same restoring force on the body irrespective of the magnitude of its deflection. Thus, the region of the bony protuberances in the buttocks floats and bears no greater weight than other areas of the buttocks, and decubitus ulcers are less likely to develop.
Nevertheless, a flotation-type cellular cushion having a flexible backing and air cells of low height to a measure tends to assume the contour of the support on which it rests. Such a cellular cushion, when placed on a sling-type wheelchair seat, might not distribute the suspension forces well enough to overcome the curvature of the seat and as a consequence the cushion may confine the occupant laterally to an excessive measure, thus forcing the occupant's thighs together in an uncomfortable manner.
The present invention resides in a light weight base or tray having generally uniform thickness throughout, insofar as the material from which it is formed is concerned, yet having ribs which impart rigidity and the desired lower contour to it. The upper surface, on the other hand, possesses a contour suitable for seating, particularly as an underlying support for a cushion, since it enhances the effective depth of immersion in the buttocks area.